1. Field of the Invention
This invention relates generally to infrared communications systems and, more specifically, to an Improved Optics System for Infrared Signal Transceivers.
2. Description of Related Art
As technology becomes continually more accessible to the "common man," the ability to use, store, transfer and otherwise manipulate information has become the focus of most businesses as well as for the individual consumer. Access to the information resources is commonly by some sort of network system, including World Wide Web, "Intranets", local area networks, wide area networks, as well as corporate databases.
While the conventional method for connecting to one of these information networks has been via cable and wire, as the reliance upon connectivity to information has deepened, the desire to gain such access from mobile or portable devices has strengthened. These portable devices, such as Personal Digital Assistants, handheld computers, and even cellular telephones are now being connected to each other and to networks via Infrared Data Communications. In fact, it is virtually impossible to purchase a notebook computer today that does not include an Infrared Data Communications assembly resident within it.
FIG. 1 depicts the typical infrared data communications hardware that is installed in electronic devices; it is a perspective view of a prior infrared transceiver assembly 10. As discussed above, these assemblies 10 are found in virtually every notebook computer sold today. The components of the assembly 10 are virtually identical across all manufacturers' product lines, with few exceptions. The typical assembly 10 comprises a housing 12 within which the infrared emitter and detector (see FIG. 2) are mounted. The "transceiver" is actually data processing circuitry for managing the emitter and detector; it's location is therefore not optically-dependent (and, in fact, it operates better in "IR darkness"). The housing 12 usually is molded from plastic, with a primary lens unit 14 formed in one of the sides of the housing 12. As can be seen, the conventional primary lens unit 14 comprises two lenses; one each for the emitter and detector (both lenses with similar optical properties, and both requiring precision and reproducibility). Adjacent to the housing 12, is a protective lens 16. The protective lens 16 is generally constructed from a colored plastic that is transparent to infrared signals. In most cases, the protective lens 16 is attached to the external case of the electronic device, its purpose being to protect the inner workings of the device, while also permitting infrared signals to pass in and out. FIG. 2 gives further detail regarding the workings of the prior assembly 10.
FIG. 2 is a cutaway side view of the prior infrared transceiver assembly 10 of FIG. 1. As can be seen, the housing 12 is generally attached to the "motherboard" 18 or other printed circuit board within the electronic device. Within the housing 12 is located an emitter/detector pair 20. It should be understood that it is also common to place more than a single emitter and/or detector inside of one housing 12 (e.g. two emitters and one detector, etc.); an emitter/detector pair 20 is used here simply in the interest of brevity.
The emitter/detector pair 20 transmit and receive infrared signals. The emitter/detector pair 20 is typically mounted to a stand 22, and thereby positioned in the signal path of the lens 14 in order to send and receive infrared signals therethrough. As discussed earlier, the appliance case 24 has an aperture 25 formed therein, and into which a protective lens 16 is installed. The protective lens 16 simply protects the inner workings of the appliance from contamination.
This prior assembly 10 has several deficiencies. First, the protrusion of the primary lens unit 14 can make the housing 12 difficult to grasp by humans and/or machines assembling the electronic devices. The difficulty in grasping can result in manufacturing defects, production delays, and generally higher costs of production. What is needed is a primary lens unit design that does not present a grasping difficulty to assemblers.
Second, the primary lens unit 14 mandates higher manufacturing and design standards than the average plastic housing for an electronic device to insure that the light-refractive traits of the lens 14 are predictable and repeatable. Because the primary lens unit 14 is integral to the housing 12, the entire housing 12 becomes subject to the elevated quality standards. It would be much more cost-effective if the design of the integral primary lens unit 14 did not mandate elevated quality standards for the entire housing 12.
Other defects with the prior assembly 10 are illuminated by FIG. 3. FIG. 3 is a cutaway side view of the transceiver assembly 10 of FIGS. 1 and 2, depicting the typical transmit dispersion angle .theta..sub.T of the assembly 10. By current IrDA (Infrared Data Association) standards, the transmit dispersion angle .theta..sub.T must be at least 15 (fifteen) degrees from the focal axis 26 (in two dimensions, of course). The transmit dispersion angle .theta..sub.T is the sum-total of the primary lens refraction angle .theta..sub.1 and the protective lens refraction angle .theta..sub.2. All prior assemblies 10 include a protective lens 16 that has no refractive power; the protective lens refraction angle .theta..sub.2 is, therefore, typically 0 degrees. Consequently, the conventional primary lens unit refraction angle .theta..sub.1 is 15 (fifteen) degrees.
There are several design implications resulting from having the entire transmit dispersion angle .theta..sub.T provided by the primary lens unit 14. The emitter/detector pair 20 must be located at the focal point 30 of the primary lens unit 14 in order to insure that no signal data is lost. As such, the height 28 (as well as horizontal placement) of the emitter/detector pair 20 is very specifically defined. Moreover, the stand (see FIG. 2) must be included in order to raise the emitter/detector pair 20 above the printed circuit board 18. It would be a better arrangement if the emitter/detector pair 20 could be mounted directly to the printed circuit board 18. Furthermore, the separation 32 between the primary lens unit 14 and the protective lens 16 is very critical. Unless the primary lens unit 14 is very close to the protective lens 16, the protective lens 16 must be relatively large or else the mandated angular dispersion will not be met. A large protective lens 16 can be a serious design constraint for the smaller electronic devices, where component real estate is very tight. What would be better is a design that permits the protective lens 16 to be very small, allows the lens separation distance 32 to be flexible, and still meets the IrDA angular dispersion requirements.